U.S. patent number 5,778,280 [Application Number 08/613,238] was granted by the patent office on 1998-07-07 for image forming apparatus which corrects for misregistration.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Naoaki Ide, Kenichi Komiya, Koji Tanimoto.
United States Patent |
5,778,280 |
Komiya , et al. |
July 7, 1998 |
Image forming apparatus which corrects for misregistration
Abstract
An image forming apparatus including a plurality of latent image
forming units for forming latent images on a plurality of image
carriers, a plurality of developing devices for forming developed
images by developing the latent images formed by the latent image
forming units, and an image conveyer belt for conveying the
developed images formed by the developing devices. The image
forming apparatus further contains a registration sensor for
detecting the developed images conveyed on the image conveyer belt,
and the registration sensor has a light source, a first optical
fiber element for guiding the light from the light source and
illuminating the image conveyer belt to obtain the reflected light,
a second optical fiber element for guiding the reflected light in a
specified direction, and a light receiving element for converting
the reflected light guided by the second optical fiber element into
an electric signal. The image forming apparatus has a computing
device for a computing misregistration correcting amount to correct
the misregistration of each of the developed images conveyed by the
image conveyer belt based on the detecting result of the
registration sensor and executes the correction of the
misregistration based on the computed result of the computing
device.
Inventors: |
Komiya; Kenichi (Kanagawa-ken,
JP), Tanimoto; Koji (Kanagawa-ken, JP),
Ide; Naoaki (Shizuoka-ken, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Kawasaki, JP)
|
Family
ID: |
13288925 |
Appl.
No.: |
08/613,238 |
Filed: |
March 8, 1996 |
Foreign Application Priority Data
|
|
|
|
|
Mar 24, 1995 [JP] |
|
|
7-065502 |
|
Current U.S.
Class: |
399/49; 347/116;
399/301 |
Current CPC
Class: |
G03G
15/0194 (20130101); H04N 1/506 (20130101); H04N
1/0473 (20130101); H04N 2201/0471 (20130101); H04N
2201/03162 (20130101); H04N 2201/04786 (20130101); H04N
2201/04722 (20130101); H04N 1/12 (20130101); G03G
2215/0119 (20130101); G03G 2215/0158 (20130101); H04N
1/193 (20130101); H04N 2201/04787 (20130101); H04N
2201/04793 (20130101); H04N 2201/04732 (20130101); H04N
2201/0471 (20130101); H04N 2201/04722 (20130101); H04N
2201/04732 (20130101); H04N 2201/04786 (20130101); H04N
2201/03162 (20130101); H04N 2201/04787 (20130101); H04N
2201/04793 (20130101) |
Current International
Class: |
H04N
1/047 (20060101); G03G 15/01 (20060101); H04N
1/50 (20060101); H04N 1/12 (20060101); H04N
1/191 (20060101); H04N 1/193 (20060101); G03G
015/00 () |
Field of
Search: |
;399/49,301 ;347/116
;358/526 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Royer; William J.
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. An image forming apparatus comprising:
a plurality of latent image forming means for forming latent images
on a plurality of image carriers;
a plurality of developing means, arranged corresponding to the
image carriers, for forming developed images by developing the
latent images formed by the latent image forming means;
means for conveying the developed images formed by the developing
means;
means for detecting the developed images being conveyed on the
image conveying means, the detecting means including a light
source, a first optical fiber element for guiding a light from the
light source and illuminating the image conveying means to obtain
reflected light, a second optical fiber element for guiding the
reflected light in a specified direction, and a light receiving
element for converting the reflected light guided by the second
optical fiber element into an electric signal;
means for computing a misregistration correcting amount to correct
misregistration of each of the developed images conveyed by the
image conveying means based on the detecting result of the
detecting means; and
means for executing correction of the misregistration based on the
computed result of the computing means.
2. An image forming apparatus as claimed in claim 1, wherein the
second optical fiber element of the detecting means is arranged in
line in a direction parallel to a moving direction of the image
conveying means against the first optical fiber element.
3. An image forming apparatus as claimed in claim 1, wherein the
second optical fiber element of the detecting means is arranged in
line in a direction orthogonal to a moving direction of the image
conveying means against the first optical fiber element.
4. An image forming apparatus as claimed in claim 1, wherein the
detecting means further includes an objective lens arranged between
a set of the first and second optical fiber elements and the image
conveying means.
5. An image forming apparatus as claimed in claim 1, wherein the
first optical fiber element and the second optical fiber element of
the detecting means are arranged with specified angle of incidence
and angle of reflection provided against a normal line which is
vertical to a plane surface of the image conveying means.
6. An image forming apparatus as claimed in claim 5, wherein the
detecting means further includes a first objective lens arranged
between the first optical fiber element and the image conveying
means and a second objective lens arranged between the second
optical fiber element and the image conveying means.
7. An image forming apparatus as claimed in claim 1, wherein the
second optical fiber element of the detecting means includes a
plurality of optical fiber elements arranged to surround the first
optical fiber element.
8. An image forming apparatus as claimed in claim 1, wherein the
second optical fiber element of the detecting means includes a
plurality of optical fiber elements arranged to surround the second
optical fiber element.
9. An image forming apparatus as claimed in claim 1, wherein the
detecting means includes a first and a second detecting unit which
are comprised of a set of the first and the second optical fiber
elements, and the first and the second detecting units are arranged
in a straight line in a direction orthogonal to a moving direction
of the image conveying means.
10. An image forming apparatus as claimed in claim 1, wherein the
detecting means includes a first and a second detecting unit which
are comprised of a set of the first and the second optical fiber
elements, and the first and the second detecting units are arranged
in a straight line in a direction parallel to a moving direction of
the image conveying means.
11. An image forming apparatus as claimed in claim 1, wherein the
detecting means includes a first and a second detecting unit which
are comprised of a plurality of sets of the first and the second
optical fiber elements, and the first detecting unit is arranged in
a straight line in a direction parallel to a moving direction of
the image conveying means, and the second detecting unit is
arranged in a straight line in a direction orthogonal to the first
detecting unit.
12. An image forming apparatus as claimed in claim 1, wherein the
detecting means includes a first detecting unit comprising a set of
the first and the second optical fiber elements and a second
detecting unit comprising a set of the first and second optical
fiber elements, the first detecting unit being arranged at one end
side in a direction orthogonal to a moving direction of the image
conveying means and the second detecting unit being arranged at the
other end side in the direction orthogonal to the moving direction
of the image conveying means.
13. An image forming apparatus comprising:
a plurality of latent image forming means for forming latent images
on a plurality of image carriers;
a plurality of developing means, arranged corresponding to the
image carriers, for forming developed images by developing the
latent images formed by the latent image forming means;
means for conveying the developed images formed by the developing
means;
means for detecting the developed images being conveyed on the
image conveying means, the detecting means including:
a common light source;
a common light receiving element for converting a light into an
electric signal;
a first detecting unit comprising a first optical fiber element, in
which one end thereof is optically connected to the common light
source and the other end thereof faces the image conveying means,
for guiding the light from the common light source and illuminating
the image conveying means to obtain reflected light, and a second
optical fiber element, in which one end thereof is optically
connected to the common light receiving element and the other end
thereof faces the image conveying means, for guiding the reflected
light to the common light receiving element; and
a second detecting unit comprising a third optical fiber element,
in which one end thereof is optically connected to the common light
source and the other end thereof faces the image conveying means,
for guiding the light from the common light source and illuminating
the image conveying means to obtain reflected light, and a fourth
optical fiber element, in which one end thereof is optically
connected to the common light receiving element and the other end
thereof faces the image conveying means, for guiding the reflected
light to the common light receiving element;
means for computing a misregistration correcting amount to correct
the misregistration of each of the developed images conveyed by the
image conveying means based on the detecting result of the
detecting means; and
means for executing correction of the misregistration based on the
computed result of the computing means.
14. An image forming apparatus as claimed in claim 13, wherein the
other ends of the first and second optical fiber elements of the
first detecting unit are arranged at one end side in a direction
orthogonal to a moving direction of the image conveying means, and
the other ends of the third and fourth optical fiber elements of
the second detecting unit are arranged at the other end side in the
direction orthogonal to the moving direction of the image conveying
means.
15. An image forming apparatus comprising:
a plurality of latent image forming means for forming latent images
on a plurality of image carriers;
a plurality of developing means, arranged corresponding to the
image carriers, for forming developed images by developing the
latent images formed by the latent image forming means;
means for conveying the developed images formed by the developing
means;
first detecting means for detecting the developed images conveyed
on the image conveying means, the first detecting means including a
first light source, at least one first optical fiber element for
guiding the light from the first light source and illuminating the
image conveying means to obtain reflected light, and at least one
second optical fiber element, which is combined with the first
optical fiber element, for guiding the reflected light in a
specified direction;
second detecting means for detecting the developed images conveyed
on the image conveying means, the second detecting means arranged
with a space to the first detecting means in a direction orthogonal
to a moving direction of the image conveying means and including a
second light source, at least one third optical fiber element for
guiding the light from the second light source and illuminating the
image conveying means to obtain reflected light, and at least one
fourth optical fiber element, which is combined with the third
optical fiber element, for guiding the reflected light in a
specified direction;
first supporting means for supporting the first detecting means
movable in the direction orthogonal to the moving direction of the
image conveying means;
second supporting means for supporting the second detecting means
movable in the direction orthogonal to the moving direction of the
image conveying means;
first moving means for moving the first supporting means along the
direction orthogonal to the moving direction of the image conveying
means;
second moving means for moving the second supporting means along
the direction orthogonal to the moving direction of the image
conveying means;
means for computing a misregistration correcting amount to correct
misregistration of each of the developed images conveyed by the
image conveying means based on the detecting results of the first
and the second detecting means;
means for executing correction of the misregistration based on the
computed result of the computing means; and
means for changing a relative position between at least either the
first or the second detecting means and the image conveying
means.
16. An image forming apparatus comprising:
a plurality of latent image forming means for forming latent images
on a plurality of image carriers;
a plurality of developing means, arranged corresponding to the
image carriers, for forming developed images by developing the
latent images formed by the latent image forming means;
means for conveying the developed images formed by the developing
means;
means for detecting the developed images being conveyed on the
image conveying means, the detecting means including a light source
for illuminating the image conveying means to obtain reflected
light, an optical fiber element for guiding the reflected light in
a specified direction, and a light receiving element for converting
the reflected light guided by the optical fiber element into an
electric signal;
means for computing a misregistration correcting amount to correct
the misregistration of each of the developed images conveyed by the
image conveying means based on the detecting result of the
detecting means; and
means for executing correction of the misregistration based on the
computed result of the computing means.
17. An image forming apparatus comprising:
image forming means for forming a prescribed image on an image
carrier;
means for detecting the prescribed image formed by the image
forming means on the image carrier, the detecting means including a
light source for illuminating the image carrier to obtain a
reflected light from the image carrier, an optical fiber element
for guiding the reflected light in a specified direction, and a
light receiving element for converting the reflected light guided
by the optical fiber element into an electric signal; and
control means for controlling the image forming means to correct a
misregistration of the prescribed image from a desired position,
where the prescribed image should be located, based on the
detecting result of the detecting means and to form an image at the
desired position.
18. An image forming apparatus comprising:
image forming means for forming a prescribed image on an image
carrier;
means for detecting the prescribed image formed by the image
forming means on the image carrier, the detecting means including a
light source, an optical fiber element for guiding a light from the
light source onto the image carrier to obtain a reflected light
from the image carrier, and a light receiving element for
converting the reflected light into an electric signal; and
control means for controlling the image forming means to correct a
misregistration of the prescribed image from a desired position,
where the prescribed image should be located, based on the
detecting result of the detecting means and to form an image at the
desired position.
19. An image forming apparatus comprising:
image forming means for forming a prescribed image on an image
carrier;
means for detecting the prescribed image formed by the image
forming means on the image carrier, the detecting means including a
light source, a first optical fiber element for guiding a light
from the light source and illuminating the image carrier to obtain
a reflected light, a second optical fiber element for guiding the
reflected light in a specified direction, and a light receiving
element for converting the reflected light guided by the second
optical fiber element into an electric signal; and
control means for controlling the image forming means to correct a
misregistration of the prescribed image from a desired position,
where the prescribed image should be located, based on the
detecting result of the detecting means and to form an image at the
desired position.
20. An image forming apparatus as claimed in claim 19, wherein the
second optical fiber element of the detecting means is arranged in
line in a direction parallel to a moving direction of the image
carrier against the first optical fiber element.
21. An image forming apparatus as claimed in claim 19, wherein the
second optical fiber element of the detecting means is arranged in
line in a direction orthogonal to a moving direction of the image
carrier against the first optical fiber element.
22. A pattern misregistration detecting apparatus comprising:
an image carrier carrying a prescribed pattern;
means for moving the image carrier in a specified direction;
means for detecting the prescribed pattern on the image carrier,
the detecting means including a light source for illuminating the
image carrier to obtain a reflected light from the image carrier,
an optical fiber element for guiding the reflected light in a
specified direction, and a light receiving element for converting
the reflected light guided by the optical fiber element into an
electric signal; and
means for obtaining an amount of misregistration of the prescribed
pattern from a desired position, where the prescribed pattern
should be located, based on the detecting result of the detecting
means.
23. A pattern misregistration detecting apparatus comprising:
an image carrier carrying a prescribed pattern;
means for moving the image carrier in a specified direction;
means for detecting the prescribed pattern on the image carrier,
the detecting means including a light source, an optical fiber
element for guiding a light from the light source onto the image
carrier to obtain a reflected light from the image carrier, and a
light receiving element for converting the reflected light into an
electric signal; and
means for obtaining an amount of misregistration of the prescribed
pattern from a desired position, where the prescribed pattern
should be located, based on the detecting result of the detecting
means.
24. A pattern misregistration detecting apparatus comprising:
an image carrier carrying a prescribed pattern;
means for moving the image carrier in a specified direction;
means for detecting the prescribed pattern on the image carrier,
the detecting means including a light source, a first optical fiber
element for guiding a light from the light source and illuminating
the image carrier to obtain a reflected light, a second optical
fiber element for guiding the reflected light in a specified
direction, and a light receiving element for converting the
reflected light guided by the second optical fiber element into an
electric signal; and
means for obtaining an amount of misregistration of the prescribed
pattern from a desired position, where the prescribed pattern
should be located, based on the detecting result of the detecting
means.
25. A pattern misregistration detecting apparatus as claimed in
claim 24, wherein the second optical fiber element of the detecting
means is arranged in line in a direction parallel to a moving
direction of the image carrier against the first optical fiber
element.
26. A pattern misregistration detecting apparatus as claimed in
claim 24, wherein the second optical fiber element of the detecting
means is arranged in line in a direction orthogonal to a moving
direction of the image carrier against the first optical fiber
element.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transfer type color image
forming apparatus which forms an image for each color component on
a plurality of photosensitive drums and superposes color images on
each other on a recording paper, and is applicable to a color laser
beam printer or a color digital copying machine.
2. Description of the Related Art
A transfer type color image forming apparatus has a first through a
fourth image forming units which form four corresponding color
images based on four image data of yellow (hereinafter, shown as
Y), magenta (a kind of red, hereinafter, shown as M), cyan (bluish
purple, hereinafter, shown as C) and black (hereinafter, shown as
B) which were decomposed according to a well-known subtractive
color process, a paper conveying mechanism for conveying paper to
retain images formed by the first through the fourth image forming
units, and a fixing device for fixing toner images on the paper
conveyed through the paper conveying mechanism.
The first through the fourth image forming units include
photosensitive drums which retain electrostatic latent images
corresponding to image data which were decomposed into respective
color components.
There are a charging device, an exposing device or an imaging bar,
a developing device and a transfer device in order in the vicinity
of each photosensitive drum. The charging device supplies a
prescribed uniform electric charge to the surface of each
photosensitive drum. The exposing device forms an electrostatic
latent image on the charged photosensitive drum by applying laser
beams corresponding to image data. An imaging bar records image
data electrostatically on each photosensitive drum. The developing
device forms a toner image by supplying a toner in color
corresponding to an electrostatic latent image formed on the
photosensitive drum. The transfer device transfers a toner image
formed on the photosensitive drum on a paper conveyed by the paper
conveying mechanism. A paper is conveyed to respective
photosensitive drums of the first through the fourth image forming
units successively and color toner images formed on respective
photosensitive drums are transferred one upon another on the
recording paper.
The paper conveying mechanism includes a conveyer belt which is
formed in an endless shape and movable in the specified direction
between the photosensitive drums of the first through the fourth
image forming units and the transfer device. By moving the conveyer
belt in the state with a paper electrostatically adsorbed thereto
at a constant speed, toner images formed by respective image
forming units corresponding to respective color components are
superposed on each other on a paper at respective transfer
positions. Further, the paper with the toner images transferred
thereon is conveyed to the fixing device at the rear stage.
The fixing device includes a pair of upper and lower heating
mechanisms and when a paper passes between these heating
mechanisms, the paper and a toner image on the paper are heated to
fuse and fix the toner image on the paper.
By the way, if toner images in respective color components are not
accurately superposed on each other successively, a misregistration
of color images is produced on this kind of transfer type color
image forming apparatus. Factors causing the misregistration of
color images may be a tilt or a misregistration of position
peculiar to the image forming unit, divergence of image forming
timing of images formed through the image forming units and a
misregistration of the transfer positions when images are
superposed on a paper.
From the above, a number of methods to detect and correct the
misregistration of color images have been so far proposed. For
instance, a method to detect a misregistration of toner images
corresponding to respective color components at a high accuracy by
a cheap optical sensor and a sensor aperture in a peculiar shape
has been disclosed in Japanese Patent Disclosure No. 06-278322. In
addition, a method to eliminate a misregistration of color images
by changing timings for forming latent images on the photosensitive
drums based on the misregistration of the detected toner images
also has been disclosed.
However, the method disclosed in the Japanese Patent Disclosure No.
06-278322 to detect the misregistration of toner images has such a
problem that a highly accurate shape of the sensor aperture and a
highly accurate mounting of the optical sensor are demanded. This
will reduce a cost of a sensor to detect a misregistration of color
images on a transfer type color image forming apparatus but
increase a cost for assembling the apparatus.
Further, as the conveyer belt of the paper conveying mechanism to
convey paper is formed using a member with a mirror surface or has
a similar reflecting characteristic in many cases, there is a
problem that the surface may be scratched by a paper and the
reflecting light is applied to a misregistration sensor as if there
is a paper. This will cause such problems that if slight flaws are
produced on the conveyer belt, a replacement of the conveyer belt
becomes necessary, thus increasing a running cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image
forming apparatus which produces no misregistration of color images
when toner images corresponding to color components are superposed
on each other.
According to the present invention, there is provided an image
forming apparatus comprising a plurality of latent image forming
means for forming latent images on a plurality of image carriers; a
plurality of developing means, arranged corresponding to the image
carriers, for forming developed images by developing the latent
images formed by the latent image forming means; means for
conveying the developed images formed by the developing means;
means for detecting the developed images being conveyed on the
image conveying means, the detecting means including a light
source, a first optical fiber element for guiding a light from the
light source and illuminating the image conveying means to obtain
the reflected light, a second optical fiber element for guiding the
reflected light in the specified direction, and a light receiving
element for converting the reflected light guided by the second
optical fiber element into an electric signal; means for computing
misregistration correcting amount to correct the misregistration of
each of the developed images conveyed by the image conveying means
based on the detecting result of the detecting means; and means for
executing correction of the misregistration based on the computed
result of the computing means.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic sectional view showing an image forming
apparatus of the present invention;
FIG. 2 is a schematic diagram showing a first embodiment of a
misregistration detecting mechanism to detect misregistration of
images, applicable to the image forming apparatus shown in FIG.
1;
FIG. 3 is a schematic block diagram showing a controller of the
image forming apparatus shown in FIG. 1;
FIGS. 4A, 4B and 4C are schematic diagrams showing examples of
respective misregistrations of images;
FIG. 5 is a schematic diagram showing a registration sensor of the
misregistration detecting mechanism shown in FIG. 2;
FIG. 6 is a schematic diagram showing an optical fiber and a range
of misregistration detecting region used in the misregistration
detecting mechanism shown in FIG. 2;
FIG. 7 is a flowchart showing one example of the operation for
rearranging image data by detecting the tilted misregistration
using the first embodiment shown in FIG. 2;
FIG. 8 is a plan view showing the principle which is able to detect
the tilted misregistration according to the first embodiment shown
in FIG. 2;
FIGS. 9A, 9B and 9C are schematic diagrams for explaining a method
to rearrange image data to correct the tilted misregistration shown
in FIG. 8;
FIGS. 10A, 10B and 10C are schematic diagrams showing examples of
driving data of imaging bars for forming image data corresponding
to image data obtained by the rearrangement of the image data shown
in FIGS. 9A, 9B and 9C;
FIG. 11A and 11B are schematic diagrams showing the operations of
the imaging bars corresponding to the driving data of respective
imaging bars shown in FIG. 10A, 10B and 10C;
FIG. 12A and 12B are schematic diagrams for explaining other
examples of a method for rearranging image data to correct the
tilted misregistration shown in FIG. 8;
FIG. 13A is a flowchart showing another example of the operation
for rearranging image data by detecting the tilted misregistration
using the misregistration detecting mechanism shown in FIG. 37;
FIG. 13B is a schematic top view showing the tilted state of an
imaging bar to a photosensitive drum of a fourth image forming
unit;
FIG. 14 is a plan view showing the principle that is able to detect
the sub-scanning misregistration according to the first embodiment
shown in FIG. 2;
FIG. 15 is a flowchart showing an example of the operation for
defining the light emitting timing of the imaging bar by detecting
the sub-scanning misregistration using the first embodiment shown
in FIG. 2;
FIG. 16 is a schematic diagram for explaining the light emitting
timing shown in FIG. 15;
FIG. 17 is a plan view showing the principle that is able to detect
the main scanning misregistration according to the first embodiment
shown in FIG. 2;
FIGS. 18A ad 18B are schematic diagrams for explaining a method to
rearrange image data for correcting main scanning misregistration
shown in FIG. 17;
FIG. 19 is a plan view showing the principle that is able to detect
main scanning misregistration according to the first embodiment
shown in FIG. 2;
FIG. 20 is a flowchart showing an example of the operation for
defining the light emitting timing of the imaging bar by detecting
sub-scanning misregistration using the first embodiment shown in
FIG. 2;
FIG. 21 is a schematic diagram showing an example of flaws produced
on a conveyer belt used in the image forming apparatus shown in
FIG. 1;
FIG. 22 is a schematic diagram showing a deformed example of a
registration sensor of the misregistration detecting mechanism
shown in FIG. 2;
FIG. 23 is a schematic diagram showing the relationship between the
direction of the light applied from the registration sensor to
flaws on the conveyer belt shown in FIG. 21 and the direction of
the light reflecting on the conveyer belt;
FIG. 24 is a schematic diagram showing the relationship between the
direction of the light applied from the registration sensor to
flaws on the conveyer belt shown in FIG. 21 and the direction of
the light reflected on the conveyer belt;
FIGS. 25A and 25B are schematic diagrams showing a second
embodiment of the misregistration detecting mechanism;
FIGS. 26A and 26B are schematic diagrams showing deformed examples
of the misregistration detecting mechanism shown in FIGS. 25A and
25B;
FIG. 27 is a schematic diagram showing a third embodiment of the
misregistration detecting mechanism;
FIG. 28A and 28B are schematic diagrams showing examples of outputs
obtained by the misregistration detecting mechanism shown in FIG.
27;
FIG. 29 is a schematic diagram showing a fourth embodiment of the
misregistration detecting mechanism;
FIG. 30A, 30B and 30C are schematic diagrams showing examples of
outputs obtained by the misregistration detecting mechanism shown
in FIG. 29;
FIG. 31 is a flowchart showing an example of the operation for
defining the exposure timing and the exposure start location of the
imaging bar by detecting the sub and main scanning misregistrations
by the misregistration detecting mechanism shown in FIG. 27;
FIG. 32 is a schematic block diagram showing the controller of the
image forming apparatus including the misregistration detecting
mechanism shown in FIG. 29;
FIG. 33 is a schematic diagram showing a fifth embodiment of the
misregistration detecting mechanism;
FIGS. 34A and 34B are schematic diagrams showing a sixth and a
seventh embodiments of the misregistration detecting mechanism;
FIG. 35 is a schematic diagram showing an eighth embodiment of the
misregistration detecting mechanism;
FIG. 36 is a schematic diagram showing a ninth embodiment of the
misregistration detecting mechanism;
FIG. 37 is a schematic diagram showing a tenth embodiment of the
misregistration detecting mechanism;
FIG. 38 is a schematic block diagram showing the controller of the
image forming apparatus including the misregistration detecting
mechanism shown in FIG. 37;
FIGS. 39A and 39B are a perspective view showing an example of
damages which may be produced on the conveyer belt by the image
forming apparatus shown in FIG. 1 and a graph showing outputs of
corresponding sensors;
FIG. 40 is a schematic diagram showing an eleventh embodiment of
the misregistration detecting mechanism; and
FIG. 41 is a schematic block diagram showing the controller of the
image forming apparatus including the misregistration detecting
mechanism shown in FIG. 40.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, preferred embodiments of the present invention will be
described in detail referring to the attached drawings.
FIG. 1 shows an image forming apparatus of the present invention.
FIG. 2 is a partial schematic diagram extracting essential
component parts of the image forming apparatus shown in FIG. 1 and
FIG. 3 is a block diagram showing an example of the controller of
the image forming apparatus shown in FIG. 1.
In FIG. 1, an image forming apparatus 1 has a first through a
fourth image forming units 10, 20, 30 and 40 and a conveyer belt 51
to convey a paper P in the arrow direction, on which images formed
by respective image forming units 10, 20, 30 and 40 are to be
transferred. The image forming units 10, 20, 30 and 40 are arranged
in series along the conveyer belt 51.
The image forming units 10, 20, 30 and 50 include photosensitive
drums 11, 21, 31 and 41 which are image carriers of which outer
surfaces are formed rotatable in the same direction at a location
contacting the conveyer belt 51.
The photosensitive drums 11, 21, 31 and 41 are arranged so that
their axial lines become orthogonal to the direction in which
images formed on respective drums are conveyed by the conveyer belt
51. Hereinafter, the direction of axial line of the photosensitive
drums will be shown as the main scanning direction and the
direction in which the photosensitive drums are rotated, that is,
the rotary direction of the conveyer belt 51 as the sub-scanning
direction.
Around the photosensitive drums 11, 21, 31 and 41, there are
charging rollers 12, 22, 32 and 42 as charging means, imaging bars
13, 23, 33 and 43 as latent image forming means, developing devices
14, 24, 34 an 44 as developing means, transfer rollers 15, 25, 35
and 45 as transfer means, and cleaners 16, 26, 36 and 46 extending
in the main scanning direction, respectively arranged in order
along the rotary direction of corresponding photosensitive drums,
respectively.
Imaging bars 13, 23, 33 and 43 are arranged so that light emitting
timings of light sources corresponding to image data can be moved
to the upstream side or the downstream side of memory areas which
are provided continuously in the sub-scanning direction according
to location information to correct tilted misregistrations of
images. Imaging bars of which luminous quantity is adjustable based
on density information shown in 16 steps, for instance, 0, 1
through 9 and A through E and F, are used.
The image forming units 10, 20, 30 and 40 form images in colors
corresponding to decomposed color components, that is, yellow
(hereinafter, shown as Y), magenta (a kind of red, hereinafter
referred to as M), cyan (bluish purple, hereinafter referred to as
C) and black (hereinafter referred to as B) images, respectively.
In this embodiment, the image forming units 10, 20, 30 and 40 are
corresponding to Y, M, C and B images, respectively and therefore,
color developers or toners corresponding to Y, M, C and B are
accommodated in the developing devices 14, 24, 34 and 44,
respectively.
The conveyer belt 51 is rotated in the arrow direction when
supporting rollers 52 and 53 are rotated counterclockwise. Further,
one of the supporting rollers 52 and 53, for instance, the
supporting roller 52 which is arranged in close vicinity to the
image forming unit 10 is rotated by a motor 54.
Under the conveyer belt 51, there is arranged a cassette 55 which
accommodates image receiving media, for instance, paper P. The
paper P accommodated in the cassette 55 is taken out of the
cassette 55 by a paper supply roller 56, which is rotated at a
specified timing, and guided to an aligning roller 58 via a feed
roller 57.
At the downstream side in the direction in which the conveyer belt
51 is rotated, there are arranged two sets of registration sensors
59 and 60 with a specified space in the main scanning direction for
detecting locations of toner images transferred to the conveyer
belt 51.
In the vicinity of the supporting roller 53, there is provided a
fixing device 61 for fixing toner images in respective colors on
the paper P, which are formed by the first through the fourth image
forming units 10, 20, 30 and 40 and superposed on each other on the
paper P on the conveyer belt 51 via the corresponding transfer
rollers 15, 25, 35 and 45. At the outside of the color image
forming apparatus 1, a tray 62 is attached for retaining the paper
P with a toner image fixed and ejected from the image forming
apparatus 1. Further, in the vicinity of the supporting roller 53,
there is arranged a belt cleaner 63 for removing paper residues,
contamination, etc. produced from toners and paper P adhered to the
conveyer belt 51.
A controller 100 of the image forming apparatus shown in FIG. 1 is
schematically shown in FIG. 3.
As shown in FIG. 3, the controller 100 of the image forming
apparatus has a CPU 101 as a main controller, a ROM 102 connected
thereto, a memory unit 103 and a non-volatile memory 104
(hereinafter referred to as NVM). The ROM 102 stores initial data
which are used for initializing the image forming apparatus. The
memory unit 103 includes a buffer memory, a page memory and a bit
map memory, stores image data input from an external apparatus (not
shown) temporarily and is used for developing image data to be
printed. The NVM 104 stores various control data computed for
correcting misregistration of color images.
A first comparator 111 for taking out an image detecting signal
from the first registration sensor 59 and a second comparator 112
for taking out an image detecting signal from the second
registration sensor 60 are connected to the CPU 101 via a first
interrupt port INTA and a second interrupt port INTB, respectively.
Further, an inverted input terminal of the first comparator 111 and
an inverted input terminal of the second comparator 112 are
connected to the CPU 101 via a first and a second D/A converters
113 and 114, respectively. Image detecting signals from the first
registration sensor 59 and the second registration sensor 60 are
also input to the CPU 101 through the first and the second A/D
converters 115 and 116, respectively.
In addition, an image data control circuit 121 and an imaging bar
driver 122 are connected to the CPU 101. The image data control
circuit 121 changes density data and location data of image data
which are supplied to the imaging bars 13, 23, 33 and 43 of the
first through the fourth image forming units for correcting
misregistration of color images. The imaging bar driver 122 has the
light sources of respective imaging bars emit light based on image
data which are changed by the image data control circuit 121.
Next, the operation of the image forming apparatus shown in FIGS. 1
through 3 will be described.
When the power switch (not shown) is turned ON, the image forming
apparatus 1 is initialized and kept in the standby state.
Hereinafter, the process for forming a Y image will be explained
referring to the first image forming unit 10. Further, needless to
say, M, C and B images are formed similarly by the second through
the fourth image forming units 20, 30 and 40.
The photosensitive drum 11 is rotated in the arrow direction and
its surface is uniformly charged by the charging roller 12. In
succession, Y image data corresponding to information to be
recorded on the specified location of the photosensitive drum 11 by
the imaging bar 13 is exposed and a Y electrostatic latent image
corresponding to the image data supplied by the imaging bar 13 is
formed on the surface of the photosensitive drum 11.
The latent image formed on the photosensitive drum 11 is developed
by the developing device 14, which is accommodating Y toner, and
converted into a Y toner image.
The Y toner image formed on the photosensitive drum 11 is
transferred on the paper P by the transfer roller 15. That is, the
paper P is taken out of the cassette 55 and aligned by the aligning
roller 58. Thereafter, the paper P is conveyed to the location
opposite to the photosensitive drum 11 while being adsorbed on the
conveyer belt 51, and the Y toner image is transferred on the paper
P by the transfer roller 15 at a location opposite to the
photosensitive drum 11.
Hereinafter, the M, C and B toner images formed on the
photosensitive drums 21, 31 and 41 by the second, third and fourth
image forming units 20, 30 and 40, respectively are superposed to
each other on the paper P that is conveyed by the conveyer belt 51.
That is, in case of printing in multiple colors, the image forming
operation of one cycle of process comprising charging, exposure,
development and transfer is executed by the image forming units 10,
20, 30 and 40 and a toner image in multiple colors are transferred.
Untransferred toners left on the photosensitive drums 11, 21, 31
and 41 are removed by cleaners 16, 26, 36 and 46, respectively.
The paper P with toner images transferred in respective colors is
separated from the conveyer belt 51, conveyed to the fixing device
61 and after the image is heated, fused and fixed by the fixing
device 61, the paper is ejected onto the tray 62.
Color toners and paper residues produced from the paper P and
adhered to the conveyer belt 51 are removed by the belt cleaner
63.
On this type of image forming apparatus, as a misregistration of
color images tends to be produced when a plurality of images formed
for every color components are superposed on the paper P, many
methods for superposing images in multiple colors have been so far
proposed. Here, causes for producing misregistration of color
images will be pursued and a method for removing the causes will be
explained.
FIGS. 4A through 4C show kinds and features of misregistrations of
color images.
A first misregistration is a directional misregistration indicated
by an arrow A as shown in FIG. 4A, which is a misregistration of an
image top line, that is, a positional misregistration in the
sub-scanning direction. A second misregistration is a directional
misregistration in the direction indication by an arrow B as shown
in FIG. 4B, which is a misregistration of the exposure starting
position, that is, a misregistration in the main scanning
direction. A third misregistration is a tilted misregistration in
both the main and sub-scanning directions as shown in FIG. 4C.
Further, in many cases it is expected that the misregistrations
shown in FIGS. 4A, 4B and 4C are produced mutually or in the all
combined state.
FIG. 5 shows one example of the registration sensors 59 and 60
shown in FIG. 2. As the registration sensors 59 and 60 are
substantially in the same construction, the registration sensor 59
will be used as a representative one in the explanation.
The registration sensor 59 has a light source 59a, a first optical
fiber 59b to guide the light from the light source 59a to a
specified location of the conveyer belt 51, and a second optical
fiber 59c to take in the light reflected on the conveyer belt 51
and illuminated by the first optical fiber 59b and guide it to an
optical sensor 59d. The optical sensor 59d is arranged in one
united body with the light source 59a or in the vicinity of the
light source 59a. The first optical fiber 59a and the second
optical fiber 59c adjoin each other in the main scanning direction
and are arranged vertical to the face of the conveyer belt 51. The
detecting range, that is, detecting accuracy of the reflecting
light from the conveyer belt 51, of the registration sensor 59 is
defined by a diameter and numerical aperture of a fiber and a
distance between the conveyer belt 51 and the end surface of the
fiber shown in FIG. 6.
FIG. 6 shows characteristics of an optical fiber suited to the
registration sensor shown in FIG. 5.
In general, an optical fiber has a core portion a and a cladding
portion b and the running direction of the light transmitted to the
inside of the fiber is changed at the interface of the core portion
a and the cladding portion b, and is propagated from the incident
side to the outgoing side.
The light output to the outside of the optical fiber from its
outgoing side is diffused at a specified angle based on the
numerical aperture NA.
In detail, the light from the light source 59a is transmitted
through the core portion a of the first optical fiber 59b and is
dispersed in a conical shape according to the numerical aperture NA
of the optical fiber when output from the first optical fiber 59b.
Similarly, when the light is input to the second optical fiber 59c,
only the light within the range of the numerical aperture NA is
guided into the optical fiber. That is, an undesired light incident
to the optical fiber is restricted by the numerical aperture NA.
Thus, the light guided by the first optical fiber 59b and the light
in the oblique lined portion which is superposed by the incident
light region are guided to the second optical fiber 59c. The
detecting accuracy of the registration sensor 59 shown in FIG. 5 is
defined by the diameters and the numerical apertures NA of the
first and the second optical fibers and a distance between the
apertures of the fibers and the conveyer belt 51.
From the above, if the outer diameter of an optical fiber is 500
.mu.m, the diameter of the core portion a of the optical fiber is
480 .mu.m, the numerical aperture NA is 0.5, and a distance between
the end surface of the optical fiber and the conveyer belt 51 is
0.5 mm, the detecting accuracy becomes about 557 .mu.m. As optical
fibers in outer diameter of several .mu.m are easily obtained, it
is possible to achieve a high level of detecting accuracy by
optimizing the combination.
Next, a method to remove a misregistration of color images formed
by the image forming units 10, 20, 30 and 40 of the image forming
apparatus 1 will be described.
When the image forming apparatus 1 is set in the adjusting mode
through an operating panel (not shown), the first through the
fourth image forming units 10, 20, 30 and 40 are instructed by the
CPU 101 to print a test pattern. In this adjusting mode, the paper
P is not conveyed from the cassette 55 by the paper supply roller
56 and the conveyer belt 51 only is rotated at a specified
speed.
First, in connection with the tilted misregistration shown in FIG.
4C, a deviation of parallelism between the imaging bars of
respective image forming units and corresponding photosensitive
drums or a deviation of right angle between respective image
forming units and the moving direction of the conveyer belt are
detected.
In detail, a first and a second test pattern images T.sub.L1 and
T.sub.R1 comprising a plurality of dot patterns lined up in the
main scanning direction are formed at the location corresponding to
the vicinity of the first and the second registration sensors 59
and 60 of the conveyer belt 51 by the fourth image forming unit 40
as shown in FIG. 2.
That is, the photosensitive drum 41 of the fourth image forming
unit 40 is charged by the charging roller 42 to a specified
potential under the control of the CPU 101. In succession, a pair
of left and right test patterns L.sub.L1 and L.sub.R1 are exposed
on the photosensitive drum 41 with a specified space in the main
scanning direction at the same exposure timing by the imaging bar
43.
The first and the second test patterns L.sub.L1 and L.sub.R1
exposed on the photosensitive drum 41 are converted into an
electrostatic latent image on the photosensitive drum 41. This
electrostatic latent image is guided to the developing device 44
with the rotation of the photosensitive drum 41 and is converted
into a first and a second test pattern images T.sub.L1 and T.sub.R1
as color images corresponding to the test patterns by a developing
device 44.
The first and the second test pattern images T.sub.L1 and T.sub.R1
formed on the photosensitive drum 41 are conveyed to the transfer
station opposite to the conveyer belt 51 with the rotation of the
photosensitive drum 41 and are transferred on the conveyer belt 51
via the transfer roller 45. In the adjusting mode, the paper P is
not used and the first and the second test pattern images T.sub.L1
and T.sub.R1 are transferred directly on the conveyer belt 51. The
adjusting mode may be set by another method, for instance, the
adjusting mode is set when the image forming apparatus is warmed
up, is performed after each of a few hundred copying operations or
is supplied with power.
The first and the second test pattern images T.sub.L1 and T.sub.R1
transferred on the conveyer belt 51 are moved to the fixing device
61 side with the rotation of the conveyer belt 51 and are guided
into the detecting region opposite to the first and the second
registration sensors 59 and 60.
The first test pattern image T.sub.L1 conveyed by the conveyer belt
51 passes through the detecting region comprising the first optical
fiber 59b and the second optical fiber 59c of the first
registration sensor 59. The reflecting light from the conveyer belt
51 and the test pattern image T.sub.L1 taken out by the second
optical fiber 59c when passing through this detecting region is
photoelectrically converted by the optical sensor 59d and input to
the non-inverted input terminal of the first comparator 111.
Further, the output from the CPU 101 for defining a first threshold
level TH1 is converted to an analog signal via the D/A converter
113 and input to the inverted input terminal of the first
comparator 111. As a result, the output satisfying the first
threshold level TH1 is input to the first comparator 111 from the
first registration sensor 59 and an interrupt signal is input to a
port PA and a first interrupt port INTA of the CPU 101.
On the other hand, the test pattern image T.sub.R1 passes through a
detecting region formed by the first optical fiber 60b which guides
light from a light source 60a and the second optical fiber 60c of
the second registration sensor 60. The reflecting light from the
conveyer belt 51 and the test pattern image T.sub.R1 taken out by
the second optical fiber 60c when passing through this detecting
region is photoelectrically converted by the optical sensor 60d and
input to the non-inverted input terminal of the second comparator
112. Further, the output from the CPU 101 for defining the first
threshold level TH1 is converted to an analog signal via the D/A
converter 114 and input to the inverted input terminal of the
second comparator 112. As a result, the output satisfying the first
threshold level TH1 is input to the second comparator 112 from the
second sensor 60 and an interrupt signal is input to a port PB and
a second interrupt port INTB of the CPU 101.
Accordingly, a time from the moment when the first and the second
test pattern images T.sub.L1 and T.sub.R1 formed by the imaging bar
of a corresponding image forming unit (here, the first image
forming unit is taken as an example) were exposed until the first
and the second test pattern images T.sub.L1 and T.sub.R1 were
developed, transferred on the conveyer belt 51 and passed through
the first and the second registration sensors 59 and 60 is
accurately measured via the CPU 101. As shown in the flowchart in
FIG. 7, at the point of time when the first and the second test
pattern images T.sub.L1 and T.sub.R1 formed by the fourth image
forming unit 40 were detected by the first and the second
registration sensors 59 and 60, a degree of tilt against standard
values of the first and the second test pattern images T.sub.L1 and
T.sub.R1 in the main scanning direction, that is, the degree of
tilt against the conveyer belt 51 of the first image forming unit
10 is computed from a time difference between a previously detected
test pattern image and a successively detected test pattern image.
If time difference =0 is satisfied, there is no tilt.
In connection with the third, second and first image forming units
30, 20 and 10, tilts of test pattern images T.sub.L2 and T.sub.R2,
T.sub.L3 and T.sub.R3, and T.sub.L4 and T.sub.R4 against the
standard values in the main scanning direction are computed,
respectively according to the flowchart shown in FIG. 7.
That is, test patterns (latent images) are recorded on the
photosensitive drum 11 by the imaging bar 14 and at the same time,
the CPU 101 starts the time measurement (ST701) using a first and a
second timers (not shown) in the CPU.
The test patterns (latent images) are developed by the developing
device 14 and a developed toner image is transferred on the
conveyer belt 51.
When the output of the first registration sensor 59, that is, an
interrupt signal was input to the CPU 101 through the first
interrupt port INTA, the CPU 101 terminates the time measurement by
the first timer (not shown) and stores a measured time t1 in a
built-in memory (ST702, ST711 and ST712).
Then, when the output of the second registration sensor 60, that
is, an interrupt signal was input to the CPU 101 through the second
interrupt port INTB, the CPU 101 terminates the time measurement by
the second timer and stores a measured time t2 in the memory
(ST713, ST714 and ST715).
The CPU 101 computes a tilt from a time difference of the measured
times (ST709).
For instance, as t2>t1, assuming that an angle of tilt is
.theta., a space between the detecting locations of the first and
the second registration sensors 59 and 60 is L, and a process speed
(a progressing speed of the belt) is V, the tilt .theta. is
computed according to the following expression.
The CPU 101 stores this angle of tilt in the built-in memory
(ST710).
Further, when the output of the second registration sensor 60, that
is, an interrupt signal was input to the CPU 101 through the second
interrupt port INTB, the CPU 101 terminates the time measurement by
the second timer and stores the measured time t2 in the memory
(ST703, ST704 and ST705).
Then, when the output of the first registration sensor 59, that is,
an interrupt signal was input to the CPU 101 through the first
interrupt port INTA, the CPU 101 terminates the time measurement
and stores the measured time t1 in the memory (ST706, ST707 and
ST708).
The CPU 101 computes a tilt from a time difference of the measured
times (ST709) and stores an angle of tilt in a memory built in the
CPU 101 (ST710).
Further, when the output of the first registration sensor 59, that
is, an interrupt signal and the output of the second registration
sensor 60, that is, an interrupt signal were input to the CPU 101
simultaneously through the first interrupt port INTA and the second
interrupt port INTB, respectively, the CPU 101 judges that there is
no tilt (ST716 and ST717).
The operations described above are repeated up to the imaging bar
43 of the fourth image forming unit 40 (ST718).
When completing the operations described above up to the imaging
bar 43 of the fourth image forming unit 40, the CPU 101 computes
image data so as to eliminate a tilt of each imaging bar
(.theta.=0) and output a change amount to the image data control
circuit 121. The image data control circuit 121 rearranges data on
the built-in image data memory according to this change amount
(ST719).
That is, with the first and the second registration sensors 59 and
60 arranged at both ends of the conveyer belt 51 as shown in FIG.
2, if there is a time difference when test pattern images pass
through respective sensors, a tilt (the degree of parallelism) of
the imaging bars can be detected by the previously described
process shown in the flowchart in FIG. 7.
As described above, the tilts of the first through the fourth image
forming units 10, 20, 30 and 40 are all detected and the tilts of
respective image forming units against the rotary direction of the
conveyer belt 51 are stored in the specified address in the memory
unit 103. This tilt is converted into an image data correction
amount by the CPU 101 according to a computing routine stored in
the ROM 102 and stored in the NVM 104.
Here, the image data correction amount to be stored in the NVM 104
and tilts of images formed by the image forming units will be
explained.
For instance, assuming that the imaging bar 43 of the fourth image
forming unit 40 was arranged not parallel to the main scanning
direction as shown in FIG. 8, the second test pattern image
T.sub.R1 transferred on the conveyer belt 51 is detected by the
second registration sensor 60 before the first test pattern image
T.sub.L1 .
It may be regarded that, for instance, image data originally
arranged parallel to the main scanning direction in a specified
memory area sized 16 dots in the main scanning direction and 1 dot
in the sub-scanning direction as shown in FIG. 9A were stored as if
they were arranged in the tilted state as shown in FIG. 9B. The
concept of the tilt of this image data is applicable to all cases
where the imaging bar only is tilted, the photosensitive drum only
is tilted and the image forming unit only is tilted.
From the above, when the tilt of a test pattern image is detected
according to the flowchart shown in FIG. 7, likewise the
arrangement obtained by superposing a straight line which is
originally expressed by a memory area less tilt on a tilted memory
area in the oblique lined state as shown in FIG. 9C, images to be
output to the conveyer belt 51 can be formed parallel to the main
scanning direction by moving image data in the memory area in the
sub-scanning direction by a specified amount in a memory storage
area adapting to the detected degree of tilt.
FIGS. 1OA through lOC show the imaging bar driving data for driving
the imaging bars, which replaced the image data stored in the
memory area shown in FIGS. 9A through 9C. That is, when a 3
lines-16 rows (16 dots) local memory is defined and a straight line
in the density F at 1 through 16 rows of the second line of the
memory area is recorded as shown in FIG. 9A, if there is no tilt as
shown in FIG. 10A, an image parallel to the main scanning direction
is formed by simply providing density information as shown in FIG.
10A. On the contrary, if the straight line is tilted by 1 dot in
the sub-scanning direction at its right end as shown in FIG. 9B, it
can be regarded that the imaging bar driving data also has a tilt
as shown in FIGURE 10B. From this, an imaging bar driving data
corresponding to image data which are shifted in a memory area are
formed as shown in FIGURE lOC when density information and location
information are combined. The location information u and 1 show
that image data shown by specified density information are moved to
the upstream side or the downstream side of an adjacent memory area
in the sub-scanning direction as described later referring to FIGS.
11A and 11B.
Shown in FIGS. 11A and 11B are typical diagrams showing the
relationship between the light emitting state (the light emitting
time) of the light emitting elements of the imaging bars 13, 23, 33
and 43 incorporated in the first through the fourth image forming
units and the imaging bar driving data shown in FIG. 10C.
In FIGS. 11A and 11B, the light emitting state of the imaging bar
corresponding to the imaging bar driving data for 1 dot in the
memory area is shown.
As explained in the above, the density information shows the light
emitting times of 16 steps shown by 0, 1, . . . 9, A . . . E and F
and, for instance, "A" shows that the light emitting time is 11/16.
Further, the location information shows 2 types of operations shown
by u and 1 and "u" shows the light emissions continuous at the
upstream side of memory areas continuous in the sub-scanning
direction and "1" shows the light emissions continuous at the
downstream side of memory areas which are continuous in the
sub-scanning direction.
From the above, if the imaging bar driving data supplied to some
light source of the imaging bar are "A, u", the light is emitted
for a length "A" continuously to the upstream side of the
continuous memory areas as shown in FIG. 11A. If the imaging bar
driving data are "A, 1", the light is emitted for a length "A"
continuously to the downstream side of the continuous memory areas
as shown in FIGURE 11B.
Shown in FIGS. 12A and 12B are typical diagrams showing the imaging
bar driving data shown in FIGS. 10A through 10C deformed to
correspond to the actual exposing length in the main scanning
direction. That is, if the number of light sources of the imaging
bars in the main scanning direction is "n", as image data having 1
dot width in the sub-scanning direction recorded in the memory area
are shown as in FIG. 12A, the density information and the shift
amount of the location information depending on the tilt are
proportionally distributed based on the number of dots "n" in the
main scanning direction and thus, the tilt in the main scanning
direction is eliminated.
Secondly, in connection with the sub-scanning misregistration shown
in FIG. 4A, deviations between the imaging bars of the image
forming units and the mounting positions of the corresponding
photosensitive drums or deviations of spaces among the image
forming units are detected. The misregistration in the sub-scanning
direction will be explained hereinafter taking the state where the
misregistration of tilt was removed as explained referring to FIGS.
7 through 12B as an example. As the misregistration of tilt was
already eliminated, it is possible to detect the sub-scanning
misregistration by a test pattern image at either side and the
corresponding registration sensor and so, hereinafter, the first
registration sensor 59 will be explained as a representative
sensor.
FIG. 14 is a schematic diagram showing the relationship of position
between a test pattern image T.sub.L comprising a plurality of dot
patterns formed and lined up by one of the first through the fourth
image forming units 10, 20, 30 and 40 and the first registration
sensor 59.
The test pattern image TL transferred on the conveyer belt 51 is
guided to the detecting region opposite to the first registration
sensor 59 with the movement of the conveyer belt 51 in the same
manner as the detecting of the tilted misregistration as explained
in the above using FIGS. 7 through 12. The test pattern image
T.sub.L conveyed by the conveyer belt 51 passes through the
detecting region by the first optical fiber 59b and the second
optical fiber 59c of the first registration sensor 59. During this
passage, the reflecting light from the conveyer belt 51 and the
test pattern image T.sub.L taken out by the second optical fiber
59c is converted photoelectrically by the optical sensor 59d and
input to the non-inverted input terminal of the first comparator
111. The output from the CPU 101 for defining the threshold level
is converted to an analog signal through the D/A converter 113 and
input to the inverted input terminal of the first comparator 111.
Here, it is assumed that a time from when the first test pattern
image is formed by the imaging bar 13 of the first image forming
unit 10 until it passes through the first registration sensor 59 is
T1 second.
In succession, the second test pattern image (not shown) comprising
a plurality of dot patterns lined up in the sub-scanning direction
is formed by the second image forming unit 20 in the same manner as
above. Further, the third and the fourth test pattern images
comprising a plurality of dot patterns lined up in the sub-scanning
direction are formed in order.
Here, after forming the second through the fourth test pattern
images by the second, the third and the fourth image forming units
20, 30 and 40, a time for each test pattern image to pass through
the first registration sensor 59 is computed in order according to
the flowchart shown in FIG. 15.
At this time, as the second through the fourth test pattern images
formed on the conveyer belt 51 by the second through the fourth
image forming units pass through the first registration sensor 59
after T2, T3 and T4 seconds, timings for actually exposing the test
pattern images on the photosensitive drums 21, 31 and 41 of the
second through the fourth image forming units 20, 30 and 40 are
defined to be T1-T2, T1-T3 and T1-T4 seconds, respectively based on
the exposure start timing to the first image forming unit 10 as
shown in FIG. 16.
That is, as shown in the flowchart in FIG. 15, a test pattern (a
latent image) is formed on the photosensitive drum 11 by the
imaging bar 13 of the first image forming unit 10. At the same
time, the CPU 101 starts the time measurement using a built-in
timer (not shown) in the CPU 101 (ST1501). This test pattern (a
latent image) is developed by the developing device 14 and
transferred on the conveyer belt 51, and this developed test
pattern image is conveyed. When detecting the test pattern image
transferred on the conveyer belt 51, the first registration sensor
59 outputs the sensor output and inputs this sensor output signal
into the CPU 101 through the first interrupt port INTA as an
interrupt signal (ST1502).
When receiving the interrupt signal, the CPU 101 terminates the
time measurement by the built-in timer (ST1503).
The CPU 101 stores the measured time T1 by the timer in a built-in
memory (not shown) in the CPU 101 (ST1504).
These steps ST1501 through ST1504 are repeated up to the imaging
bar 43 of the last fourth image forming unit 40. The measured times
T1, T2, T3 and T4 are stored in the memory built in the CPU 101
(ST1505).
The CPU 101 computes T1-T2, T1-T3 and T1-T4 and based on the light
emitting timing of the imaging bar 13 of the first image forming
unit 10, sets the light emitting timing for the image forming from
the next time at after [T1-T2] for the imaging bar 23 of the second
image forming unit 20, after [T1-T3] for the imaging bar 33 of the
third image forming unit 30 and after [T1-T4] for the imaging bar
43 of the fourth image forming unit (ST1506)
That is, when actually forming an image, it becomes possible to
bring the top lines of respective colors to agree with each other
by setting the exposure start timing after the second color at a
time passed from the exposure start of the first color by T1-T2,
T1-T3 and T1-T4 seconds, respectively. That is, it is possible to
correct the misregistration in the sub-scanning direction.
The exposure start timings of the first through the fourth image
forming units 10, 20, 30 and 40 relative to the sub-scanning
direction thus obtained are stored in the NVM 104 via the CPU
101.
Thirdly, in connection with the main scanning misregistration shown
in FIG. 4B, a deviation between the imaging bars of the image
forming units and the mounting locations of corresponding
photosensitive drums or a deviation of a space between the image
forming units is detected. The image misregistration in the main
scanning direction will be explained in the following taking the
state with the misregistration of tilt explained using FIGS. 7
through 12B and the image misregistration in the sub-scanning
direction described in the above referring FIGS. 14 through 16
removed, respectively as an example.
The image misregistration in the main scanning direction is
considered to be caused when the light sources of the imaging bars
13, 23, 33 and 43 of the first through the fourth image forming
units are mutually or at least one of them is deviated in the main
scanning direction as shown in FIG. 17. Further, this concept of
image data deviation in the main scanning direction is applicable
to any one of cases where the imaging bars only are
misregistrationed in parallel with the main scanning direction, the
entire image forming units are misregistrationed in parallel with
the main scanning direction and both of these cases are produced
simultaneously.
This image misregistration in the main scanning direction may be
regarded as such image data were stored, for instance, as if the
entire memory area was arranged in the state where it was moved in
parallel with the main scanning direction although image data were
stored in the specified sized memory area at the same location as
shown in FIG. 18A. From this, the misregistration in the main
scanning direction can be easily removed by shifting a region of a
memory area, in which image data are stored, corresponding to the
detected deviation as shown in FIG. 18B.
In detail, as shown in FIG. 19, a test pattern image T.sub.L formed
in the order of, for instance, the first row (a light source a),
the second row (a light source b), the third row (a light source
c), . . . is guided to a detecting region opposite to the first
registration sensor 59 with the moving of the conveyer belt 51 by
one of the first through the fourth imaging bars 13, 23, 33 and 43
(here, the imaging bar 43 of the fourth image forming unit 40 is
used as a representative). Here, the test pattern image T.sub.L of
a row corresponding to any light source conveyed by the conveyer
belt 51 passes through the detecting region comprising the first
optical fiber 59b and the second optical fiber 59c of the first
registration sensor 59 when it is brought to agree with the
detecting region of the first registration sensor 59. When passing
through this detecting region, the reflecting light from the
conveyer belt 51 taken by the second optical fiber 59c is converted
photoelectrically by the optical sensor 59d and input to the
non-inverted input terminal of the first comparator 111.
Hereinafter, test pattern images are formed in order by the third,
the second and the first image forming units 30, 20 and 10
according to the flowchart shown in FIG. 20, the misregistration of
the write start position in the main scanning direction, that is, a
phase difference is computed and further, a correction amount is
defined.
That is, a test pattern (a latent image) is formed on the
photosensitive drum 11 by the imaging bar 13 of the first image
forming unit 10. This test pattern is formed by the first dot of
the imaging bar 13. The test pattern (the latent image) is
developed by the developing device 14 and the developed toner image
is transferred on the conveyer belt 51.
If the test pattern comprising the toner image transferred on the
conveyer belt 51 is not detected by the first registration sensor
59, the CPU 101 forms the test pattern by the second dot of the
imaging bar 13 (by shifting one dot in the main scanning direction)
and repeats the step ST2001 (ST2002 and ST2003).
Further, when detecting the test pattern, the first registration
sensor 59 outputs the sensor output and inputs this sensor output
as an interrupt signal to the CPU 101 through the first interrupt
port INTA (ST2002).
When receiving the interrupt signal, the CPU 101 stores the
luminous dots which formed the detected test pattern in the memory
unit 103 (ST2004).
The steps ST2001 through ST2004 are repeated up to the imaging bar
43 of the fourth image forming unit 40. The luminous dots of
respective imaging bars which formed the test pattern detected by
the first registration sensor 59 are stored in the memory unit 103
(ST2005).
The CPU 101 transmits an image data change amount (that is, a phase
difference) to the image data control circuit 121. The image data
control circuit 121 shifts image data on the memory unit 103
according to the received image data change amount (ST2006).
As explained above, according to the first embodiment shown in
FIGS. 1 through 20, various factors causing misregistrations of
color images attributable to the misregistration and tilt of
position among the first through the fourth image forming units 10,
20, 30 and 40, the tilt and eccentricity of the photosensitive
drums in respective image forming units and the tilt of the imaging
bars in respective image forming units can be surely removed by the
first and the second registration sensors 59 and 60 arranged with a
specified distance in the main scanning direction.
As shown in FIG. 21, many scratches F may be produced on the
conveyer belt 51 along the sub-scanning direction, that is, the
moving direction of the conveyer belt 51 when a paper P passes.
From this, as shown in FIG. 22, undesired change of a size of
detecting signal detected by the second optical fiber caused by the
change in reflection factor due to scratches F on the conveyer belt
51 is prevented when the direction of scratches F on the conveyer
belt 51, the directions of the first and the second optical fibers
of the first and the second registration sensor 59 and 60 and the
moving direction of the conveyer belt 51 are specified to the
parallel direction.
FIGS. 23 and 24 are partial cross-sectional views for explaining
the relationship between the direction in which the illuminating
light is applied to the conveyer belt 51 by the first optical fiber
of the registration sensor and the moving direction of the conveyer
belt 51.
As shown in FIG. 23, likewise the first embodiment already
explained in FIG. 5, if the illuminating light is applied along the
moving direction of the conveyer belt 51, that is, the main
scanning direction orthogonal to the sub-scanning direction, the
reflecting direction of the light reflected on the conveyer belt 51
may largely change due to the depth of scratch F on the conveyer
belt 51.
On the other hand, as shown in FIG. 24, when the illuminating light
is applied from the moving direction of the conveyer belt 51, that
is, the sub-scanning direction, the reflecting direction of the
light reflected on the conveyer belt 51 can be maintained nearly
constant.
When the first and the second optical fibers of the registration
sensor are lined up in the sub-scanning direction, it becomes
possible to stabilize the signal detected by the second optical
fiber.
FIGS. 25A and 25B show a second embodiment of the registration
sensor. As two sets of the substantially same registration sensors
are arranged with a space in the main scanning direction, the
second embodiment will be explained using one set of sensors as a
representative.
In the second embodiment shown in FIG. 25A, there are provided a
plurality of second optical fibers 159b which take in the
reflecting light from the conveyer belt and guide to an optical
sensor (not shown) around a first optical fiber 159a which guides
the light from a light source (not shown) to a specified location
on the conveyer belt., The first and the second optical fibers 159a
and 159b are arranged vertically to the surface of the conveyer
belt, respectively. Now, a region wherein the conveyer belt is
illuminated by the group of optical fibers shown in FIG. 25A will
be considered. The light applied to the conveyer belt by the first
optical fiber 159a is diffused in a uniform extent on the conveyer
belt. Further, the reflecting light from the conveyer belt is
almost uniformly applied to the second optical fibers 159b
surrounding the first optical fiber 159a. Therefore, it is possible
to detect a test pattern image stably without increasing mounting
accuracy of respective optical fibers unnecessarily.
That is, according to the arranging method of the first and the
second optical fibers shown in FIG. 25A, the detecting output is
maintained constant even when the mounting directions of the first
and the second optical fibers are changed.
FIG. 26A shows a deformed example of the registration sensors shown
in FIG. 25A.
In the deformed example shown in FIG. 26A, around the second
optical fiber 159b which takes in the reflecting light from the
conveyer belt and guides it to an optical sensor (not shown), there
are arranged a plurality of first optical fibers 159a which guide
the light from a light source (not shown) to a specified location
on the conveyer belt. In this example, as the surroundings of the
second optical fiber 159b are illuminated, the reflected light from
the conveyer belt by the light applied to the conveyer belt by the
first optical fibers 159a is surely applied to the second optical
fiber 159b as shown in FIG. 26B. In this case, the quantity of
reflected light detected is more stabilized when compared with the
arrangement of the optical fibers shown in FIG. 25A.
FIG. 27 shows a third embodiment of the registration sensor. As two
sets of substantially the same registration sensors are provided
with a space in the main scanning direction, the third embodiment
will be explained here using one set of sensors as a
representative.
The registration sensors shown in FIG. 27 are arranged in at least
2 sets comprising the first optical fiber 59b and the second
optical fiber 59c in the main scanning direction. The first optical
fiber 59b which guides the light from a light source (not shown) to
the conveyer belt and the second optical fiber 59c which guides the
reflecting light from the conveyer belt to an optical sensor (not
shown) are provided alternately.
FIG. 28A is a schematic diagram showing a characteristic of the
detecting signal which is output from the registration sensor shown
in FIG. 27. FIG. 28A shows the detecting output from the
registration sensor and FIG. 28B shows the detecting output of the
registration sensor shown in FIG. 5 for the purpose of
comparison.
When FIG. 28A is compared with FIG. 28B, the detecting output of
the registration sensor when detecting a test pattern image T.sub.L
and the surface of the conveyer belt increases almost
proportionally to the number of sets of the first and the second
optical fibers. Accordingly, only when a space sufficiently enough
for installing 2 or 5 sets of fibers is secured, it becomes
possible to detect a test pattern image stably.
FIG. 29 shows a fourth embodiment of the registration sensor. As
two sets of the substantially same registration sensors are provide
with a space in the main scanning direction, the fourth embodiment
will be explained here using one set of the registration sensors as
a representative.
The registration sensors shown in FIG. 29 are arranged in 4 sets
comprising the first and the second optical fibers 59b and 59c in
the main scanning direction and 3 sets in the sub-scanning
direction. The first optical fiber 59b which guides the light from
a light source (not shown) and the second optical fiber 59c which
guides the reflecting light from the conveyer belt to an optical
sensor (not shown) are arranged alternately.
FIGS. 30A through 30C show the relationship of locations between
the registration sensor shown in FIG. 29 and a test pattern image
T.sub.VH and the level of the output signal from the registration
sensor. When the registration sensor shown in FIG. 29 is used, both
the misregistrations in the main scanning direction and the
sub-scanning direction can be detected by a same misregistration
detecting routine according to a flowchart shown in FIG. 31. In
addition, such a detecting circuit as shown in FIG. 32, which is a
deformed detecting circuit of that shown in FIG. 3, is used.
In detail, when the test pattern image T.sub.VH is passing through
one of the first and the second registration sensors 359 and 360, a
part of the region of the test pattern image T.sub.VH extending in
the sub-scanning direction is detected by the sensor. Here, the
first registration sensor 359 and the first comparator 111 will be
explained. The detailed explanation of the second registration
sensor 360 and the second comparator 112 will be omitted as they
are substantially identical to the first registration sensor 359
and the first comparator 111.
If a sensor output exceeding the first threshold level TH1 supplied
from the D/A converter 113 is input to the non-inverted input
terminal of the first comparator 111 by the first registration
sensor 359, an interrupt signal is input to the port PA and the
interrupt port INTA of the CPU 101 from the first comparator
111.
Here, the CPU 101 measures a time from when a portion of the test
pattern image T.sub.VH in the sub-scanning direction was exposed
and the output of the first comparator 111 is input to the port PA
by the imaging bar which outputs the test pattern image which is a
subject of measurement. At the same time, while the output from the
first comparator 111 is continued, that is, the CPU 101 is being
interrupted, it is judged whether the output is from a third
comparator 117.
If the output from the third comparator 117 is input to the CPU
101, the sensor output exceeding the second threshold level TH2
supplied from the third D/A converter 119 is input to the
non-inverted input terminal of the third comparator 117 by the
first registration sensor 359 as shown in FIG. 30A. As a result,
the CPU 101 judges that the test pattern image T.sub.VH has agreed
with the arrangement of the optical fiber of the first registration
sensor 359.
As a matter of course, if no output was input to the CPU 101 from
the third comparator 117, it is judged that the test pattern image
T.sub.VH does not agree with the arrangement of the optical fiber
of the first registration sensor 359 as no signal exceeding the
second threshold level TH2 is input as shown in FIG. 30B or 30C. If
the test pattern image T.sub.VH agreed with the arrangement of the
optical fiber of the first registration sensor 359, that is, when a
signal exceeding the second threshold level TH2 is input to a third
interrupt port INTC and the port PC, the CPU 101 stores the row
wherein the luminous dot of the imaging bar recorded a region in
the main scanning direction of the test pattern image T.sub.VH in
the NVM 104. Similarly, the output of the fourth comparator 118 is
input to the CPU 101 through a fourth interrupt port INTD by the
threshold level TH2 from the fourth D/A converter 120.
In more detail, as shown in FIGS. 30B, 30A and 30C in order, the
locations of dots illuminating the region in the main scanning
direction of the test pattern image T.sub.VH is moved by one row
and the luminous dot locations where the test pattern image
T.sub.VH agrees with the arrangement of the optical fibers of the
first registration sensor 359 are detected.
As described above, the CPU 101 measures phase differences of the
imaging bars in the main scanning and sub-scanning directions.
Further, this operation is repeated up to the second through the
fourth imaging bars according to the flowchart shown in FIG. 31 and
furthermore, at the point of time when phase differences of all
imaging bars are detected, the exposing timing in the sub-scanning
direction and the exposure start position of respective imaging
bars are input to the NVM 104.
That is, the CPU 101 clears n of the memory unit 103, that is, n
=0. Reference mark n denotes the number of luminous dots to record
the region extended in the sub-scanning direction of the test
pattern image T.sub.VH and finally, denotes the number of luminous
dots agreed with the aperture (ST3101).
The CPU 101 counts up the number of dots by adding 1 to n of the
memory unit 103. That is, the CPU 101 instructs the image data
control circuit 121 to shift the luminous dots for recording the
region extended in the sub-scanning direction of the test pattern
image T.sub.VH by one dot in the main scanning direction
(ST3102).
The CPU 101 instructs an imaging bar driver 122 to light the test
pattern and the imaging bars record the test pattern on the
photosensitive drums. Further, at the same time, the CPU 101 starts
the time measurement (ST3103).
The test pattern image T.sub.VH is conveyed by the conveyer belt 51
and detected by the first registration sensor 359, and a sensor
output signal is output. This sensor output signal is input to the
non-inverted input terminal of the first comparator 111 and
compared with the first threshold level TH1 by the first comparator
111. If the sensor output is less than or equal to TH1, an
interrupt signal is input to the CPU 101 through the first
interrupt port INTA (FIG. 30B). On the other hand, if the sensor
output is greater than or equal to TH1, no interrupt signal is
input to the CPU 101 and the steps ST3102 through ST3104 are
executed again (ST3104).
When an interrupt signal is input to the CPU 101 through the first
interrupt port INTA, the CPU 101 terminates the time measurement
(ST3105).
Furthermore, the test pattern image T.sub.VH is conveyed by the
conveyer belt 51 and detected by the first registration sensor 359,
and the sensor output signal is output. This sensor output signal
is input to the non-inverted input terminal of the third comparator
117 and compared with the second threshold level TH2 by the third
comparator 117. If the sensor output is less than or equal to TH2,
an interrupt signal is input to the CPU 101 through the third
interrupt port INTC (FIG. 30A). On the other hand, if the sensor
output is greater than or equal to TH2, no interrupt signal is
input to the CPU 101 and the steps ST3102 through ST3107 are
executed again (ST3106).
When an interrupt signal is input to the CPU 101 through the third
interrupt port INTC, the CPU 101 stores the measured time in the
memory unit 103 (ST3107).
Further, the CPU 101 stores a luminous dot (the n-th dot) agreed
with the aperture in the memory unit 103 (ST3108).
The CPU 101 judges whether the steps ST3101 through ST3109 have
been executed on all the imaging bars and executes the steps ST3101
through ST3109 for the imaging bar for which the steps were not
executed (ST3109).
When the above steps have been executed/completed, the CPU 101
reads the luminous dots agreed with the apertures of respective
imaging bars and computes a phase difference of each imaging bar.
Based on the result of this computation, the CPU 101 determines the
shift amount of image data of each imaging bar and instructs the
image data control circuit 121 to shift image data. The image data
control circuit 121 shifts image data according to the instruction
by the CPU 101 (ST3110).
Further, the CPU 101 reads a measured time of each imaging bar from
the memory unit 103, adjusts the light emitting timing of each
imaging bar and stores the adjusted light emitting timing of each
imaging bar in the memory unit 103. When performing the printing,
make the printing based on the light emitting timings stored in the
memory unit 103 (ST3111).
FIG. 33 shows a fifth embodiment of the registration sensor.
As shown in FIG. 33, an objective lens (a convex lens) 59e having a
specified focal distance is arranged between the first and second
optical fibers 59b and 59c arranged in a row and the conveyer belt
51.
FIGS. 34A and 34B show a sixth and a seventh embodiments of the
registration sensor. As shown in FIG. 34A, the registration sensor
is comprised of a plurality of the second optical fibers 159b
arranged around the first optical fiber 159a and an objective lens
(a convex lens) 59e having a specified focal distance arranged
between the optical fibers 159a, 159b and the conveyer belt 51.
Such the construction containing the objective lens (the convex
lens) 59e is also applicable to a registration sensor using a
plurality of the first optical fibers 159a arranged around the
second optical fiber 159b as shown in FIG. 34B.
According to the registration sensor shown in FIGS. 33, 34A and
34B, when a magnification of the objective lens (the convex lens)
59e is set at an optimum level, it becomes possible to prevent the
light incoming surface of the second optical fiber and the light
outgoing surface of the first optical fiber of the registration
sensor from being contaminated by toner or residues of paper P
which may scatter in the vicinity of the conveyer belt 51. That is,
even when, for instance, the outer diameters, core diameters and
the numerical apertures of the first and the second optical fibers
are made small in order to improve detecting accuracy, a detecting
region will become large if a distance between the fiber openings
and the conveyer belt surface becomes large. Therefore, it is
desirable that the fiber openings are arranged as close as to the
belt surface. However, the fiber openings may be contaminated by
toners on the belt surface and residues of paper P or dust and the
like. Further, there is also such a problem that unfixed toner may
adhere to the openings of the optical fibers when a paper jamming
is caused. In this case, it may become impossible to detect a test
pattern.
According to the registration sensor shown in FIGS. 33, 34A and
34B, as it becomes possible to move the fiber openings away from
the conveyer belt surface, the secular change of sensitivity of
image detecting is reduced.
FIG. 35 shows an eighth embodiment of the registration sensor. This
registration sensor has the first optical fiber 259b arranged
rectilinearly along the sub-scanning direction, that is, the
running direction of the conveyer belt and the second optical fiber
259c which detects the reflecting light from a region illuminated
by the illuminating light from the first optical fiber 259b.
Further, on the end surface of the first optical fiber 259b at the
side opposite to the conveyer belt 51, a light source 259a is
arranged. In addition, at the end surface of the second optical
fiber 259c at the side opposite to the conveyer belt 51, there is
arranged an optical sensor 259d which photoelectrically converts
the light guided by the second optical fiber 259c.
According to the registration sensor shown in FIG. 35, as the first
and the second optical fibers 259b and 259c are arranged at an
angle of tilt .theta..sub.E and .theta..sub.D to the normal line L
that is vertical to the plane surface of the conveyer belt 51, more
stabilized output is obtained.
FIG. 36 shows a ninth embodiment of the registration sensor. This
registration sensor has objective lenses 259e and 259f arranged
between the first and the second optical fibers 259b and 259c of
the registration sensor shown in FIG. 35 and the conveyer belt
51.
According to this ninth embodiment, the detecting accuracy is
improved and the secular change of sensitivity of image detecting
is prevented for the same reason as in the example explained above
referring to FIGS. 33 and 34.
FIG. 37 is a schematic diagram showing a tenth embodiment of a
misregistration detecting mechanism differing from the
misregistration detecting mechanism shown in FIG. 2. Further, the
misregistration detecting mechanism shown in FIG. 37 may be
incorporated in the image forming apparatus shown in FIG. 1 instead
of the misregistration detecting mechanism.
As shown in FIG. 37, the misregistration detecting mechanism has a
light source 555 and an optical sensor 556 which photoelectrically
converts the reflecting light from the conveyer belt 51, which is
the illuminating light generated by the light source 555 and
returned by the optical fiber shown below.
Between the light source 555 and the optical sensor 556, there are
a first and a second registration detecting portions 557 and 558
arranged with a specified distance in the main scanning
direction.
The first registration detecting portion 557 has a first optical
fiber 557a which guides the light from the light source 555 to a
specified location of the conveyer belt 51, and a second optical
fiber 557b which guides the light guided to the conveyer belt 51 by
the first optical fiber 557a and reflected thereon to the optical
sensor 556.
The second registration detecting portion 558 has a third optical
fiber 558a which guides the light from the light source 555 to a
specified location of the conveyer belt 51, and a fourth optical
fiber 558b which guides the light guided to the conveyer belt 51 by
the third optical fiber 558a and reflected thereon to the optical
sensor 556.
That is, the first registration detecting portion 557 comprises the
first optical fiber 557a, in which one end thereof is optically
connected to the light source 555 and the other end thereof faces
the conveyer belt 51 for guiding the light from the light source
555 and illuminating the conveyer belt 51 to obtain the reflected
light, and the second optical fiber. 557b, in which one end thereof
is optically connected to the optical sensor 556 and the other end
thereof faces the conveyer belt 51 for guiding the reflected light
to the optical sensor 556.
Further, the second registration detecting portion 558 comprises
the third optical fiber 558a, in which one end thereof is optically
connected to the light source 555 and the other end thereof faces
the conveyer belt 51 for guiding the light from the light source
555 and illuminating the conveyer belt 51 to obtain the reflected
light, and the fourth optical fiber 558b, in which one end thereof
is optically connected to the optical sensor 556 and the other end
thereof faces the conveyer belt 51 for guiding the reflected light
to the optical sensor 556.
Hereinafter, the tilt described above is detected on all of the
first through the fourth image forming units according to the
flowchart shown in FIG. 13A (see FIGS. 37 and 38).
The imaging bar driver 122 records a first test pattern L.sub.L1 on
the photosensitive drum 41 by the imaging bar 43 of the fourth
image forming unit according to the instruction by the CPU 101. At
the same time, the CPU 101 starts the time measurement. The first
test pattern L.sub.L1 is developed by the developing device 44 and
further, transferred on the conveyer belt 51 as the first test
pattern image T.sub.L1 by the transfer roller 45 (ST1301).
The CPU 101 terminates the time measurement after .DELTA.t Sec. has
passed (ST1302).
Then, after terminating the time measurement, the CPU 101 records a
second test pattern L.sub.R1 by the imaging bar 43 likewise the
step ST1301 (ST1303).
The first test pattern image T.sub.L1 is conveyed by the conveyer
belt 51 and detected by the first registration detecting portion
557, and the sensor output signal is output. This sensor output
signal is input to the CPU 101 through the first interrupt port
INTA as an interrupt signal (ST1304).
When the interrupt signal is input to the first interrupt port
INTA, the CPU 101 starts the time measurement (ST1305).
The second test pattern image T.sub.R1 is conveyed by the conveyer
belt 51 and detected by the second registration detecting portion
558, and the sensor output signal is output. This sensor output
signal is input to the CPU 101 through the first interrupt port
INTA as an interrupt signal (ST1306).
When the interrupt signal is input to the first interrupt port
INTA, the CPU 101 terminates the time measurement (ST1307).
The CPU 101 judges whether a time t measured according to the steps
ST1305 through ST1307 is t=.DELTA.t, and if t=.DELTA.t, judges that
there is no tilt and if t.notident..DELTA.t, judges that there is a
tilt (ST1308).
When judging that there is a tilt, the CPU 101 computes a tilt by a
time difference as described later (ST1309).
The tilt computed by the CPU 101 is stored in the memory unit 103
(ST1311).
The CPU 101 judges whether the steps ST1301 through ST1310 were
executed on all the imaging bars and executes the steps ST1301
through ST1310 for the imaging bar for which the above steps were
not executed (ST1311).
After executing the steps ST1301 through ST1310 for all the imaging
bars, the CPU 101 computes image data changing amount of the
imaging bars of the first through the fourth image forming units
according to the method descried in FIGS. 9A through 12B. This
image data changing amount is input to the image data control
circuit 121. Further, the image data control circuit 121 rearranges
image data corresponding to respective imaging bars (ST1312).
The tilt in ST1309 is computed and detected as described below.
FIG. 13B is a top view showing the photosensitive drum 41 of the
fourth image forming unit 40 and the tilt of the imaging bar 43
when viewed from the top of the imaging bar. In this example, a
case is assumed, wherein the right side of the running direction of
the conveyer belt, that is, the second registration detecting
portion 558 is tilted based on the left side of the running
direction of the belt, that is, the first registration detecting
portion 557 side.
If a time from when the first test pattern image T.sub.L1 is
detected by the first registration detecting portion 557 until the
second test pattern image T.sub.R1 is detected by the second
registration detecting portion 558, that is, a time measured by the
CPU 101 in the steps ST1304 through ST1307 shown in FIG. 13A is t,
the tilt .theta. is expressed by the following expression:
where,
Vp: Velocity of the outer surface of the photosensitive drum (equal
to the moving velocity of the conveyer belt).
L: Maximum printing region of the imaging bar.
.DELTA.t: A time difference for recording the first test pattern
L.sub.L1 and the second test pattern L.sub.R1 by the imaging
bar.
In the above example, it is judged that the imaging bar is tilted
in the following direction in FIG. 13B.
t=.DELTA.t: No tilt (Reference Numeral 43 in FIG. 13B)
t<.DELTA.t: The direction reverse to the belt running direction
(Reference Numeral 43b in FIG. 13B)
t>.DELTA.t: The belt running direction (Reference Numeral 43a in
FIG. 13B)
As described above, at A t seconds after the first test pattern
image T.sub.L1 is formed at a position corresponding to either the
first registration detecting portion 557 or the second registration
detecting portion 558 as shown by the dotted line in FIG. 37 by one
of the first through the fourth image forming units 10, 20, 30 and
40, the second test pattern image T.sub.R1 is recorded at the
position corresponding to the remaining registration sensor. If a
time difference t is "t=.DELTA.t" when the test pattern images
T.sub.L1 and T.sub.R1 are detected by the first and the second
registration detecting portions 557 and 558, it can be detected
that there is no tilt.
FIG. 38 shows a detecting circuit adaptable to the misregistration
detecting mechanism shown in FIG. 37.
The first test pattern image T.sub.L1 is passed through an
illuminating region of the first optical fiber 557a of the first
registration detecting portion 557 by the detecting circuit shown
in FIG. 38. When passing this illuminating region, the reflecting
light from the conveyer belt 51 taken out by the second optical
fiber 557b is photoelectrically converted and input to the
non-inverted input terminal of the first comparator 111. Further,
the second test pattern image T.sub.R1 is passed through the
illuminating region of the first optical fiber 558a of the second
registration detecting portion 558. When passing this illuminating
region, the reflecting light from the conveyer belt 51 taken out by
the second optical fiber 558b is photoelectrically converted and
similarly, input to the non-inverted input terminal of the first
comparator 111.
Thus, under the condition that there is no misregistration in the
main scanning direction, the positions of the first and the second
test pattern images T.sub.L1 and T.sub.R1 are easily detected by
the detecting circuit shown in FIG. 38.
By the way, as already explained in FIG. 21, a number of scratches
F may be produced on the conveyer belt 51 along the sub-scanning
direction. Further, as shown in FIG. 39A, such scars as x, y and z
which provide an undesirable reflecting light to the first and the
second registration sensors may be produced on the conveyer belt
51.
As the scars x, y and z shown in FIG. 39A are output as signals
having sufficient level when compared with the threshold level TH1
as shown in FIG. 39B, it is substantially required to exchange the
conveyer belt 51.
However, the exchange of the conveyer belt 51 has such a problem
that the image forming apparatus is made unusable for an extended
period of time.
FIG. 40 shows an eleventh embodiment of a misregistration detecting
mechanism which is differing from the misregistration detecting
mechanism shown in FIGS. 2 and 37. Further, the misregistration
detecting mechanism shown in FIG. 40 may be incorporated in the
image forming apparatus shown in FIG. 1 instead of the
misregistration detecting mechanism shown in FIGS. 2 and 37.
As shown in FIG. 40, this misregistration detecting mechanism has a
first and a second registration detecting portions 459 and 460
which are arranged with a specified distance in the main scanning
direction.
The first and the second registration detecting portions 459 and
460 are used in the registration sensors in any shape shown in many
embodiments already explained, for instance, the registration
sensor shown in FIG. 22. The first and the second optical fibers
incorporated in respective registration sensors, the light source
and the optical sensor are substantially identical to those in the
examples shown in FIG. 2 and therefore, the detailed explanation
will be omitted.
The first and the second registration detecting portions 459 and
460 are supported movable in the main scanning direction by sensor
supporters 71 and 72. The sensor supporters 71 and 72 are moved to
the specified positions in the main scanning direction through a
first and a second sensor moving mechanisms 73 and 74, which are
represented by a linear driving mechanism or a straight driving
mechanism.
FIG. 41 shows a detecting circuit adaptable to the misregistration
detecting mechanism shown in FIG. 40.
In the detecting circuit shown in FIG. 41, in the state where the
conveyer belt 51 only is running prior to the forming of the test
pattern images T.sub.L1 and T.sub.R1 on the conveyer belt 51, at
least when the conveyer belt 51 is running for more than one turn,
the outputs of the first and the second comparators 111 and 112 are
monitored.
In detail, if such scars as shown in FIG. 39A are produced on the
conveyer belt 51, the output signal from either the first or the
second registration detecting portion 459 or 460 or both detecting
portions becomes a signal at a level which is hardly discriminated
from the threshold level TH1 as shown in FIG. 39B.
In this case, the CPU 101 will judge that there are undesirable
scars on the conveyer belt 51 assuming that there is no test
pattern image formed.
If any scar was detected on the conveyer belt 51, motors 75 and 76
for moving the sensor supporter 71 or 72 supporting a corresponding
registration detecting portion in the main scanning direction are
moved by a specified distance in any direction by a corresponding
motor driver 131 or 132. In succession, while the conveyer belt 51
is running at least more than one rotation, the outputs of the
first and the second comparators 111 and 112 are monitored and the
scar of the conveyer belt 51 corresponding to the moved position is
checked.
Here, under the condition that scars of the conveyer belt 51 are
not detected, the test pattern images T.sub.L1 and T.sub.R1 are
formed successively on the conveyer belt 51 and misregistrations
are detected likewise the already explained embodiments. On the
other hand, if scars on the conveyer belt 51 were detected, the
corresponding registration detecting portions are further moved
within a movable range by the first and the second sensor moving
mechanisms 73 and 74. If any region having no scar is not detected
on the conveyer belt 51 within the movable range by the first and
the second sensor moving mechanism 73 and 74, the motor 54 is
stopped by the control of the CPU 101, a service call is displayed
on the display unit (not shown) and the exchange of the conveyer
belt 51 is instructed.
As described above, according to the image forming apparatus of the
present invention, images formed on a plurality of photosensitive
drums which are provided corresponding to respective decomposed
colors by the imaging bars which form latent images on the
photosensitive drum image carriers and converted into toner images
corresponding to respective color components through developing
devices are transferred on the conveyer belt and conveyed by the
conveyer belt, and deviations from standard values are computed by
the first and the second registration sensors. Thus, it becomes
easy to detect factors for misregistrations of color images
produced when toner images corresponding to color components are
superposed in the image forming apparatus, which are represented by
tilts between respective photosensitive drums and imaging bars
corresponding thereto, tilts between respective photosensitive
drums and the conveyer belt, deviations in distance between the
positions of respective photosensitive drums and deviations between
rotary directions of respective photosensitive drums and the
conveyer belt and directions orthogonal to the rotary
directions.
Further, if scratches or scars are produced on the conveyer belt,
which may provide undesired detecting outputs to the first and the
second registration sensors, the first and the second registration
sensors are moved optionally to positions where only a desired
output signal is provided by the conveyer belt as they are formed
movable in the direction orthogonal to the rotary direction of the
conveyer belt. Thus, factors for misregistrations of color images
which may be produced when toner images are superposed in the image
forming apparatus can be detected precisely.
On the basis of the factors for misregistrations of color images
thus obtained, when positions of image data in the memory supplied
to the specified light sources of the imaging bars and successive
light emitting timings between the light sources and the adjacent
light sources are changed based on the light emitting timings of
the imaging bars and image data, misregistrations of color images
of output images can be removed easily.
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